Recovery times and vertical speed

Background: Investigation of vertical velocity and recovery times in harbour porpoise (time between dives) and potential relationship with dive depth (longer recovery times for deeper dives). Dive threshold = 5 m. Analysis on high resolution dataset (n=5).

1 Recovery time vs depth

1.1 All

Figure 1.1: Recovery time (time between end of dive t and dive t+1) according to depth class for the 5 porpoises (high resolution tags).

Recovery time increases with dive depth.

1.2 Per individual

Figure 1.2: Individual recovery times according to depth class.

Similar pattern across individuals.

1.3 Per light cycle

Figure 1.3: Recovery time (time between end of dive t and dive t+1) according to depth class for the 5 porpoises (high resolution tags).

Similar pattern across light phases.

1.4 Per month

Figure 1.4: Recovery time according to depth class and month.

Similar pattern across months.

1.5 0-10 m, across months

## 
##  Kruskal-Wallis rank sum test
## 
## data:  dat$recovery and dat$month
## Kruskal-Wallis chi-squared = 355.54, df = 5, p-value < 2.2e-16

Figure 1.5: Recovery time according to month for dives between 0-10 m.

1.6 10-20 m, across months

## 
##  Kruskal-Wallis rank sum test
## 
## data:  dat$mean_reco and dat$month
## Kruskal-Wallis chi-squared = 5, df = 5, p-value = 0.4159

Figure 1.6: Recovery time according to month for dives between 10-20 m.

1.7 20-50 m, across months

## 
##  Kruskal-Wallis rank sum test
## 
## data:  dat$mean_reco and dat$month
## Kruskal-Wallis chi-squared = 3, df = 3, p-value = 0.3916

Figure 1.7: Recovery time according to month for dives between 20-50 m.

1.8 50-100 m, across months

## 
##  Kruskal-Wallis rank sum test
## 
## data:  dat$mean_reco and dat$month
## Kruskal-Wallis chi-squared = 4, df = 4, p-value = 0.406

Figure 1.8: Recovery time according to month for dives between 50-100 m.

1.9 100-400 m, across months

## 
##  Kruskal-Wallis rank sum test
## 
## data:  dat$mean_reco and dat$month
## Kruskal-Wallis chi-squared = 4, df = 4, p-value = 0.406

Figure 1.9: Recovery time according to month for dives between 100-400 m.

1.10 Correlation

## 
##  Pearson's product-moment correlation
## 
## data:  sum2$maxdep and sum2$recovery
## t = 128.22, df = 247475, p-value < 2.2e-16
## alternative hypothesis: true correlation is not equal to 0
## 95 percent confidence interval:
##  0.2458876 0.2532765
## sample estimates:
##       cor 
## 0.2495857

Figure 1.10: Correlation between recovery time and max depth.

Both variables are highly correlated(cor test: 0.56, p<0.001).

2 Recovery time vs duration

2.1 All

Figure 2.1: Recovery time (time between end of dive t and dive t+1) according to dive durtaion for the 5 porpoises (high resolution tags).

Recovery time increases with dive duration, but breaking point around 1 min.

2.2 Per individual

Figure 2.2: Individual recovery times according to dive durtaion.

Similar pattern across individuals.

2.3 Geom_hdr

Figure 2.3: Individual recovery times according to dive duration.

3 Hourly dives

## [1] 17.40985

## [1] 6.70212

On average 17 (SD: 6.6) dives performed per hour, including 3.3 (SD: 1.2) dives between 0-20 m and 3.8 (SD: 1.7) dives deeper than 100 m. Note dives shorter tan 20 sec and shallower than 5 m were discarded.

3.1 Mean N dives (facet_grid)

Figure 3.1: Mean daily number of hourly dives according to max depth (dive threshold: 5 m).

Shallow dives above 20 m dominate (>10 per hour), and no clear pattern is evidenced as these dives are performed all day long. Dives between 20-50 m are performed mostly during daytime, especially for individuals 22850b, 27262 and 93100. Dives deeper than 50 m are less frequent (<5 dives per hour), and a clear diel pattern was observed as these deep dives get more frequent at night, especially for individuals 22850b, 27262 and 93100.

3.2 Mean N dives

Figure 3.2: Mean daily number of hourly dives according to max depth (dive threshold: 5 m).

3.3 Frequency

Figure 3.3: Porportion of hourly dives according to max depth.

3.4 Mean N dives across months

Figure 3.4: Mean daily number of hourly dives according to max depth and months (dive threshold: 5 m).

4 Vertical speed

4.1 Ascent rate

Figure 4.1: Average ascent rate (m/s) according to depth class.

Ascent rate is higher at greater depths.

4.2 Ascent rate monthly

Figure 4.2: Average ascent rate (m/s) according to depth class and month.

4.3 Descent rate

Figure 4.3: Average descent rate (m/s) according to depth class.

Similar pattern for descent rate higher for deeper dives.

4.4 Descent rate monthly

Figure 4.4: Average descent rate (m/s) according to depth class and month.

4.5 Ascent and descent rates

Figure 4.5: Vertical speed (m/s) according to descent (orange) and ascent (green) phase and depth class.

5 Bottom time

## # A tibble: 25 × 3
## # Groups:   id [5]
##    id     class     mean_bottom_time
##    <chr>  <fct>                <dbl>
##  1 22849b (0,10]               0.197
##  2 22849b (10,20]              0.228
##  3 22849b (20,50]              0.324
##  4 22849b (50,100]             0.476
##  5 22849b (100,400]            0.335
##  6 22850b (0,10]               0.216
##  7 22850b (10,20]              0.220
##  8 22850b (20,50]              0.336
##  9 22850b (50,100]             0.552
## 10 22850b (100,400]            0.361
## # … with 15 more rows

Figure 5.1: Individual bottom duration (in min) according to depth class.

Bottom time increases with dive depth until 100 m, but then decreases for dives deeper than 100 m.

6 Vertical speed per dive type

6.1 Ascent rate

Figure 6.1: Average ascent rate (m/s) according to dive type.

6.2 Ascent rate monthly

Figure 6.2: Average ascent rate (m/s) according to dive type and month.

6.3 Descent rate

Figure 6.3: Average descent rate (m/s) according to dive type.

6.4 Descent rate monthly

Figure 6.4: Average descent rate (m/s) according to dive type and month.

6.5 Ascent and descent rates

Figure 6.5: Vertical speed (m/s) according to descent (orange) and ascent (green) phase and dive type.

7 Descent rate for deep dives (type 3)

ADL estimated at 5.4 min for a 28 kg porpoise (Reed et al 2000).

ADL estimated at 4.5 min for a 37 and 48 kg porpoise (Otani et al 2000).

Range of ADL estimated: 2.2-5 min (using body mass & metabolic rates from Rojano-Donate et al 2020).

ADL estimated at 2.2 min for a 26 kg porpoise (McDonald et al 2021). ADL estimated at 3.0 min for a 30 kg porpoise (McDonald et al 2021). ADL estimated at 4.2 min for a 44 kg porpoise (McDonald et al 2021). ADL estimated at 6.3 min for a 67 kg porpoise (McDonald et al 2021).

7.1 vs maxdep

Figure 7.1: Descent rate according to max depth for deep dives (type 3).

7.2 vs duration

Figure 7.2: Descent rate according to dive duration for deep dives (type 3).

8 Ascent rate for deep dives (type 3)

8.1 vs maxdep

Figure 8.1: Ascent rate according to max depth for deep dives (type 3).

8.2 vs duration

Figure 8.2: Ascent rate according to dive duration for deep dives (type 3).